The treadwear rating of a tire is the number listed on a tire's sidewall that states how well the tire wears compared to other tires. If a tire has a 200 rating, it wears twice as long as a tire with a rating of 100.
Treadwear ratings typically range from about 100 to 700, and the National Highway Traffic Safety Administration uses this system to provide consumers with an overall idea of how well tires wear. The ratings can be somewhat deceptive, though, as they are only an accurate comparison for tires operating under the exact same conditions. Additionally, only all-weather and summer tires are rated, not snow tires or other types of tires.